Based on research, a lot of pros like the Godox PB820. BP820? I ordered one to use with a Canon550EX at events. I will report in this forum if there is any problem. Cowboy Studio supplies Amazon with units at a bit of a discount over the $$ direct with the Dallas outfit. Be aware that many of the sellers -- even in the Amazon interface -- will not ship the Godox over water. I am in Hawaii and I had trouble finding one that would ship here. ALSO -- watch the ads carefully as some of the sellers do not include a pack-to-flash cord. These are different for various systems.

Quantum always was a very good brand for external battery packs a while back. For a while Quantum was the only player in after-market fast recycle packs.

I don't mind paying the price premium for Quantum Turbo batteries. I had a couple of original Turbos that ran flawlessly for 12 years. There was cell replacement at around six years. I literally wore out the physical casings (leather back then...) They were replaced with Quantum T2 with the twin outlets. I have never been able to run this flat. having two outlets is cool if you're running two bodies with on-camera flash. I also have a smaller Turbo SC to keep power up to off-camera 580EXII.

When your professional reputation depends on having 100% reliable gear that you never, ever have to question, cheaping-out may lose you a client. That's much more expensive than paying a few hundred dollars more for the best.

Shot one event with a new Godox BP820 and I performed well plugged into a Canon 580EX. Several hundred shots over the night and no apparent loss of charge based on array of "status" lights. (ETTL and manual)

VictorI am a happy owner of 1DsIII & 1Dx and 600ex system... So happy with my 600s that I am using them way more than I used my previous flash guns... putting aside 7b and Pro Acute systems.I have been using the Canon CP E4 battery packs to power my 600EX units.the CP E4 packs hold 8X AAs ... light weight and preform well for most small to mid jobs.because they are Canon the weather seals on the power plugs are great... Ive actually used the combo in very damp situations... heavy mist to some blasts of heavy rain.what canon does not have is battery level indicators... in either the flash or batt packs.the downside to the CP E4s are they always need batteries. I personally do not like rechargeable AAs. they do not last long and if sitting uncharged longer than a day... they just loose charge.

I recently did lots of research and went with Quantum Turbo 3 and the SC.the Quantum units cost more and are quite larger than the Canon packs BUT.they recycle FAST and keep on going.when quick recycle times are a must... the Quantum packs preform,,! especially the Turbo 3recharge times from full discharge are about 2-3 hours for the SC and 3-4 hours for the Turbo3the downside to the Quantum units are: they are heavy... not like my old Lumedyne super cyclerbut yah you feel it on your belt. the units are not weather resistant... if working in drizzle or rainsome bagging or grommets should help.... last when you unplug the unit it turns off automaticly...I have my batts because of weight behind me on my belt so its hard to turn on pack and to get response that its on...other than the obvious lights that show unit on... a beep would have been nice... especially for 400 and 650$ per unit with cables...BUT- I love them... they preform lickety fast... maybe over kill for small jobs shooting slow pace..but for any job you will need to bang hard and fast YES YES ! QUANTUM baby!